A variety of industrial processes generate effluent gases that contain carbon dioxide (CO2) and other products containing carbon, such as carbon monoxide (CO). Examples of such effluent gases include those from the steel manufacturing industry (e.g., blast furnace gas, oxygen converter gas, or coke oven gas). These effluent gases have a CO2 gas concentration ranging from about 10 to 50 volume percent (vol. %) and a CO gas concentration ranging from about 10 to 80 vol. %. Effluent gases can also contain other gases such as hydrogen, hydrocarbons and/or inert gases such as nitrogen in quantities up to about 50 vol. %. Flue gases are an example of effluent gases.
Before being emitted in to the atmosphere, CO gas in effluent gas needs to be converted to CO2 gas because of its toxicity. A combustion process can be used to produce the CO2 gas along with heat that can be used in a variety of processes. High concentrations of CO2 gas and nitrogen gas, however, significantly reduce the caloric concentration of the CO gas present in the effluent gas, resulting in a decreased incentive to use the effluent gas. Nevertheless, toxic/harmful CO gas must be converted to CO2 gas before being emitted. Hence, effluent gas is often combusted to convert the CO gas to additional CO2 gas with no attempt to recover the heat generated in electrical power production.
Regardless of the process, combusting the effluent gas or using the effluent gas in an energy producing process generates additional CO2 gas that is emitted into the atmosphere. In some regions, Europe for example, industries emitting large amounts of CO2 gas are taxed and/or are required to buy CO2 trading rights based on their use of CO2 gas producing feedstock, often rendering such energy producing processes uneconomical.
In an effort to minimize its release, CO2 gas can be captured and stored or used in one or more industrial processes. For example, industrial processes exist where CO2 gas is used as a feedstock. These applications, however, often require concentrated and highly purified CO2 gas. Examples of these industrial processes include the cement industry, the beverage industry (e.g., in the production of carbonated beverages), for syngas generation via the so-called dry reforming process or in combination with steam reforming, or in combination with steam reforming and partial oxidation via the so-called tri-reforming, or for use in producing methanol by chemical conversion with H2. The CO2 gas produced in the combustion processes, however, is typically not concentrated and/or pure enough to be used as a feedstock in such applications.
Processes that sequester CO2 gas from effluent gas also generally require an energy input to an extent that overall more CO2 is produced than is captured. In other words, CO2 conversion and/or sequestration processes are often thermodynamically unfavorable, which require energy input with extra CO2 formation. For example, CO2 absorption by amine-based solutions is known to be very efficient and selective to absorb CO2 gas. However, the recovery of CO2 from such solutions, also termed as the regeneration step, is highly endothermic. Therefore, this regeneration process requires energy which gives rise to additional energy consumption and consequently additional CO2 gas emissions.
There exists, therefore, a need for improvements in reducing CO2 emission from effluent gas containing CO and CO2 gases.